IJCSNS International Journal of Computer Science and Network Security, VOL.9 No.7, July 2009
37
Eliminate the Effects of Clipping Technique on the SER
performance by Recovering the Clipped Part of the OFDM
Signal
Ibrahim Ismail Al-kebsi1, Mahamod Ismail1, Kasmiran Jumari1 and T. A. Rahman2
1
Dept. of Electrical, Electronic & Systems Engineering, Faculty of Engineering, Universiti Kebangsaan Malaysia,
43600 UKM, Bangi, Selangor, Malaysia
2
Wireless communication centre, Faculty of Electrical, Universiti Technologi Malaysia,
Skudai, Johor, 81310 UTM, Johor, Malaysia
Summary
The simplest and most effective method to reduce PAPR might
be the clipping and filtering [1], but the error performance of
clipped OFDM signal is degraded due to the distortion of the
original signals. The simplest and most effective method to
reduce peak to average power ratio (PAPR) might be the
clipping and filtering, but the error performance of clipped
Orthogonal Frequency Division Multiplexing (OFDM) signal is
degraded due to the distortion of the original signals. This paper
suggests a simple solution to eliminate the degradation in the
SER performance that caused by clipping the OFDM signal at
the transmitter side by copying the clipped part of the OFDM
signal and provide it to the receiver to recover the original
signal. The delay in receiving the signal will be calculated to
insure the receiver will be able to recognize and recover the
clipped part of the original signal very well. With this proposed
method there is freedom to use low clipping ratio (CR) and
therefore it is easy to get efficient PAPR reduction. But it is
better to choose the appropriate CR to avoid wasting the
bandwidth by minimizing the amount of the copied part of the
clipped signal.
Key words:
Clipping Ratio, SER, PAPR, EVM, Power Amplifier, A/D
converter.PAPR.
1. Introduction
The basic premise of a multicarrier modulation scheme
is to break a wideband channel into multiple parallel,
typically, orthogonal narrowband channels. OFDM has
many well documented advantages including resistance to
multipath fading and high data rates [1, 2]. OFDM is an
effective transmission technique for high data rate
transmission in impulse noise and multipath fading
environments. OFDM has been employed in diverse
wired and wireless applications. For instance, in digital
audio and video broadcasting [3], digital subscriber lines
using discrete multitone [4], the wireless LAN systems,
Manuscript received July 5, 2009
Manuscript revised July 20, 2009
such as, IEEE 802:11, HIPERLAN and MMAC [5],
wireless broadband services [6] and also is a strong
candidate for next generation cellular systems [7]. One of
the limitations of using OFDM is the high peak-toaverage power ratio (PAPR) of the transmitted signal. A
large PAPR leads to disadvantages such as increased
complexity of the analog to digital converter (A/D) and
reduced efficiency of the radio frequency (RF) amplifier.
If power amplifiers are not operated with large linearpower back-offs, it is impossible to keep the out-of-band
power below imposed limits. This leads to very inefficient
amplification, expensive transmitters and causing
intermodulation among the subcarriers and undesired outof-band radiation. The Analog to Digital converters and
Digital to Analog converters are also required to have a
wide dynamic range which increases complexity. The
PAPR reduction techniques are therefore of great
importance for OFDM systems. To reduce the PAPR
different techniques were proposed. These techniques can
be categorized into the following, clipping and filtering
[8], coding [9], phasing [10], scrambling [11],
interleaving [12], and companding [13]. Coding is the
most widely used technique. Selective mapping has been
used [14] to reduce PAPR. However this resulted in a loss
of data during decoding. Partial transmit sequence (PTS)
is another method that is based on scrambling. Compared
to the previous method, this method is more effective. In
the PTS scheme, sub-carriers are partitioned into many
blocks and each block is multiplied by a constant phase
factor (codes) [15]. But this greatly reduces the number of
carriers. In [16], PAPR reduction is achieved by
deliberately introducing a limited number of errors to the
forward-error correction (FEC) encoded input bits. This
approach suffers receiver performance degradation. Each
of these above mentioned solutions had some problems
that are yet to be solved. The clipping signal scheme is
relatively simpler than others. The performance of the
clipping scheme is superior to that of the windowing
38
IJCSNS International Journal of Computer Science and Network Security, VOL.9 No.7, July 2009
TABLE I
SIMULATION PARAMETERS
signal scheme in OFDM system, because the windowing
technique distorts all signals, but the clipping technique
distorts small portion signal where the peak power
exceeds the maximum permitted power. The simple
concept behind this is to clip the power peaks that go
beyond a predetermined level. Clipping has been thought
to introduce error. But it actually depends on careful
selection of clipping level [17]. This paper will focus on
the clipping signal technique and it will propose a simple
method to recover the clipped part of the original OFDM
signal to improve the SER performance. The remainder of
the paper is organized as follows. Section 2 presents the
simulation model. Section 3 presents the simulation
results. Lastly, the conclusions are presented in Section 4.
Parameters
Channel Bandwidth
91 MHz
Modulation scheme (Mapping
scheme)
16QAM, 64QAM, and
256QAM
FFT Size (NFFT)
2048
Number of subcarriers
1705
Useful symbol duration (TU)
224 µs
Cyclic prefix or guard time ∆
1/8
Guard Time ( Tg =(1/8)* TU )
28 µs
Total symbol duration (TU +∆)
252 µs
Carrier spacing (1/ TU)
4.46 KHz
Number of OFDM symbols in
frame
68
The OFDM system model used in this work is shown
in Figure 1, a digital nonlinearity is introduced at the
transmitter and an equalization block at the receiver. The
proposed method to improve the SER performance by
copying the clipped OFDM signal as shown in figure 1 is
performed after the clipping process.
Copy of the
clipped part of
the OFDM signal
Data
Source
S/P
Symbol
Mapper
IFFT
P/S
Cyclic
Prefix
Insertion
D/A
Clipping
PA
AWGN
Data
Sink
P/S
Symbol
Detector&
Demapper
FFT
N −1
j 2πf nt
x(t ) = ∑ y n e
0 ≤ t ≤ NT
n =0
7.61 MHz
Carrier frequency
2. Simulation Model
A baseband OFDM symbol can be generated in the
digital domain before modulating on a carrier for
transmission. To generate a baseband OFDM symbol, a
serial of digitized data stream is first modulated using
common modulation schemes such as the phase shift
keying (PSK) or quadrature amplitude modulation
(QAM). These data symbols are then converted from
serial-to parallel (S/P) before modulating subcarriers.
Subcarriers are sampled with sampling rate N/Ts, where N
is the number of subcarriers and Ts is the OFDM symbol
duration. The frequency separation between two adjacent
subcarriers is 2π/N. Finally, samples on each subcarrier
are summed together to form an OFDM sample. In
OFDM, a block of N symbols, {yn, n=0,1,…,N-1}is
formed with each symbol modulating one set of N
subcarriers,{fn=0,1,…,N-1}. The N subcarriers spacing is
chosen to be orthogonal, that is fn = nΔf, where Δf =1/NTs.
Thus the complex envelope of the transmitted OFDM
signal is represented by
Values
S/P
Cyclic
Prefix
remove
A/D
+
(1)
This Matlab simulation will focus in the 2k mode of the
OFDM-DVB-T standard. This particular mode is
intended for mobile reception of standard definition DTV.
The transmitted OFDM signal is organized in frames.
Each frame consists of 68 OFDM symbols. Four frames
constitute one super-frame. Each symbol is constituted by
a set of 1705 subcarriers in the 2k mode. The specific
numerical values for the OFDM parameters for the 2k
mode are given in Table 1. A simple AWGN channel is
used as channel model.
Figure 1: OFDM system block diagram and the proposed solution
Deliberate clipping might be the simplest method to
reduce PAPR. This method limits the samples’ amplitudes
of the input OFDM signal to a predetermined value. If the
digital OFDM signals are clipped directly, the resulting
clipping noise will all fall in-band and cannot be reduced
by filtering. To address this aliasing problem, in this
simulation, the OFDM signal is oversampled by a factor
of 8. Then, the real valued bandpass samples, x, were
clipped at amplitude A as follows:
IJCSNS International Journal of Computer Science and Network Security, VOL.9 No.7, July 2009
⎧− A, if x < − A
⎪
y = ⎨ x,
if − A ≤ x ≤ A
⎪ A,
if x > A
⎩
(2)
Although the PAPR is moderately high for OFDM,
high magnitude peaks occur relatively rarely and most of
the transmitted power is concentrated in signals of low
amplitude. Therefore, the statistical distribution of the
PAPR should be taken into account. PAPR is independent
of modulation used. One way to avoid nonlinear
distortion is to operate the amplifier in its linear region.
Unfortunately such solution is not power efficient and
thus not suitable for battery operated wireless
communication applications. Minimizing the PAPR
before power amplifier allows a higher average power to
be transmitted for a fixed peak power, improving the
overall signal to noise ratio at the receiver. It is therefore
important to minimize the PAPR. The recovering process
will be performed at the receiver side after A/D converter
to avoid any reduction in the efficiency of the analog-todigital. The PAPR of a continuous-time OFDM signal
cannot be computed accurately by sampling the signal at
Nyquist rate. Hence oversampling is essential to produce
accurate PAPR estimates. As mentioned before discrete
time domain OFDM signal in this simulation is
oversampled by a factor of 8. The variation of the
envelope of a multi-carrier signal can be defined by the
peak to average power ratio (PAPR) which is given by:
2
Max ⎧⎨ x(t ) ⎫⎬
⎩
⎭
PAPR =
⎧
⎫
2
E ⎨ x(t ) ⎬
⎩
⎭
(3)
At the transmitter side, the invertible clipping method
reduces the amplitude dynamics, and thus the PAPR of
the signal that has to be amplified. This result is presented
in Complementary Cumulative Distribution Function
(CCDF) a term which is defined as follows:
CCDF (PAPR(x )) = Prob(PAPR( x) > PAPR0 )
39
the adjacent channels. Filtering after clipping is therefore
compulsory to limit this spectral regrowth and, finally, to
assure a good system performance. A cyclic prefix (CP) is
then appended to minimize interblock interference and aid
the frequency domain equalizer at the receiver. Digital-toanalog (D/A) conversion and analog filtering are
performed. The clipping process is characterized by the
clipping ratio (CR), defined as the ratio between the
clipping threshold and the root-mean square (rms) level of
the OFDM signal. However, Clipping is a nonlinear
process that leads to distortion. Without filtering, clipping
causes out-of-band radiation. Digital filtering is present to
control out-of-band radiation.
CR =
CL
rms level
(5)
where CL is the Clipping Level and CR is the clipping
ratio. The CR in this simulation has different values
depends on modulation schemes. Clipping the OFDM
signal before amplification is a simple and typical method
for the PAPR reduction [18]. Figure 2 exhibits the
concept of the proposed method of copying the clipped
part of the original OFDM signal in enlarged-time domain.
The original signal y = x(tn) at time tn is clipped by the
threshold value A to the clipped signal. The copied signal
that will be provided to the receiver side is equal to:
y_copy(tn) = ± x(tn) - (± A)
where: tn = 0:Ts, and n= 0: [Ts /(1/Sp)], and Ts is the total
OFDM symbol period, and Sp is the simulation period.
The recovered OFDM signal at the receiver side is the
received signal plus to the copied signal as follows:
y_recov(tn) = y_copy(tn)+ y_r,
where y_r is the received signal and can be defined as :
y_r = y+AWGN
Amplitude
A3
A2
A
A1
x(t3)= A3
x(t2)= A2
y_copy(t3
x(t1)=
(4)
This function represents the probability that the PAPR of
the OFDM signal exceeds the threshold PAPR0. This
invertible clipping method allows reducing the PAPR of
the OFDM signal. The implementation of deliberate
clipping is quite simple and effective in PAPR reduction,
but larger clipping ratio results in the severe SER
performance
degradation.
Unfortunately,
clipping
generates a spectral regrowth (the so called spectral
shoulders) on the spectrum of output signal, widening its
frequency support. Thus, parasitic frequencies appear in
t1
t2
t3
time
Figure 2: The clipped OFDM signal and copied signal
To understand the proposed method of recovering the
original signal, figure 3 illustrates the details of copying
IJCSNS International Journal of Computer Science and Network Security, VOL.9 No.7, July 2009
40
the clipped part of the OFDM signal and then using it to
recover the original signal at the receiver side.
OFDM symbol Mapper
Real valued bandpass OFDM
signal
y= real [x(t)]
If y > +A
or y < -A
No
Yes
or
y= +A
y = -A
y = x(t)
especially for large number of subcarriers as in this
simulation, high magnitude peaks occur relatively rarely
and most of the transmitted power is concentrated in
signals of low amplitude.
Table 2 shows the percentage of the clipped samples
of the original OFDM signals at different CR values for
various modulation schemes. The higher the clipping ratio,
few OFDM samples will be clipped. So it is important to
choose the CR carefully to get a good reduction in the
PAPR without degrade the performance of SER. But with
this proposed method of recovering the clipped part of the
original signal, it is possible to clip the signal hardly or in
other word using small CR without degrading the SER
performance.
TABLE II: PERCENTAGE OF THE CLIPPED OFDM SAMPLES AT
DIFFERENT CLIPPING RATIO VALUES
Clipping Ratio
(CR)
Modulation scheme
Percentage of
clipping %
256-QAM
16.41
Yes
y_copy=y - (± A)
If y = ± A
1.35
No
y copy= 0
2.75
64-QAM
16.37
16-QAM
15.28
256-QAM
0.99
64-QAM
0.86
16-QAM
0.80
PA
Channel
A/D
y_recov=y_copy+ y_r
OFDM symbol
Demapper
Figure 3: The proposed method to recover the clipped OFDM signal
3. Results and Discussion
When using the clipping scheme, the phase
information of the signal is completely transmitted, and
the amplitude of the signal is clipped if the power of the
signal exceeds the maximum permitted power. If using
ideal power control to counteract the influence of wireless
channel in systems and not considering other factors
(such as frequency set-off), the received signal amplitude
also shows as the same as the original signal plus to
AWGN. Although PAPR is very large for OFDM
The most important thing that should be considered in
this proposed recovering method is appropriate choosing
of the CR value. In this proposed method, a low Clipping
Ratio (CR) will achieve a significant PAPR reduction,
and improve the SER performance, but the price is
increasing in the amount of the copied signal which is in
fact a redundancy in the transmitted data.
Figure 4 (a and b) shows the clipped signal, copied
signal and the recovered signal at different CR values.
IJCSNS International Journal of Computer Science and Network Security, VOL.9 No.7, July 2009
Time response of the clipped signal
Time response of the copied part of the clipped signal
600
400
A m p li tu d e (v )
A m p li tu d e (v )
500
200
0
-200
0
-500
-400
-600
41
signal, and this is the disadvantage of using low CR in
this proposed method because it causes redundancy in the
transmitted data and wastes the available bandwidth. So it
is better to choose appropriate CR to get the advantage of
this proposed method without any sacrificing in the
bandwidth.
0
0
0.2
0.4
0.6
Time (sec)
0.8
1
0
0.2
0.4
-6
x 10
Time response of the received signal
0.6
Time (sec)
0.8
10
1
-6
x 10
Time response of therecovered signal
600
-1
1000
10
400
A m p li tu d e (v )
0
-200
-2
10
0
SER
A m p li tu d e (v )
500
200
-500
-400
-600
0
0.2
0.4
0.6
Time (sec)
0.8
-1000
1
0
0.2
0.4
-6
x 10
0.6
Time (sec)
0.8
-3
10
1
-4
-6
x 10
10
Original OFDM signal
Clipped signal (CR=1)
Recovered signal (CR=1)
Clipped signal (CR=2.5)
Recovered signal (CR=2.5)
(a)
-5
10
Time response of the copied part of the clipped signal
800
600
600
400
400
A m p l itu d e (v )
A m p l itu d e (v )
Time response of the clipped signal
800
200
0
-200
-400
2
200
4
6
8
10
SNR (dB)
12
14
16
18
Figure 5: SER performance of the original, clipped, and recovered
OFDM signal using proposed method of OFDM -16QAM
0
-200
-400
-600
-600
0
-800
0
0.2
0.4
0.6
Time (sec)
0.8
-800
1
0
0.2
0.4
-6
x 10
Time response of the received signal
0.6
Time (sec)
0.8
10
1
-6
x 10
-1
Time response of the recovered signal
10
800
1000
600
500
A m p l i tu d e (v )
200
0
-200
-2
10
0
SER
A m p l i tu d e (v )
400
-500
-400
-3
10
-600
-1000
-800
0
0.2
0.4
0.6
Time (sec)
0.8
1
0
-6
x 10
0.2
0.4
0.6
Time (sec)
0.8
1
-4
-6
x 10
(b)
10
Original OFDM signal
Clipped signal (CR=1.3)
Recovered signal (CR=1.3)
Clipped signal (CR=2.7)
Recovered signal (CR=2.7)
-5
10
Figure 4: Time response of the clipped, copied, received, and recovered
signal of OFDM-256QAM at two different clipping ratio CR (a) CR=1.2,
(b) CR=2.3
Figures 5, 6, and 7 show the ability of the proposed
method to improve the performance of the SER. It is easy
to note that the improvement in the SER of the recovered
OFDM signal at different CR values is better than the
SER performance of the conventional clipped OFDM
signal and it shows superior performance compared to the
normal or unclipped OFDM signal. The proposed method
was tested with different modulation schemes such as 16,
64, and 256QAM, and in all schemes the performance of
the SER at low CR values is better than that with high CR
values. This is because in the hard clipping, more peaks
will be clipped and this means more copies of clipped
parts of the original signal will be transmitted as
information data to the receiver to recover the original
5
10
15
SNR (dB)
20
25
30
Figure 6: SER performance of the original, clipped, and recovered
OFDM signal using proposed method of OFDM -64QAM
IJCSNS International Journal of Computer Science and Network Security, VOL.9 No.7, July 2009
42
0
The transmitted OFDM signal
10
1000
a m p lit u d e
500
-1
10
0
-500
SER
-1000
0
0.1
0.2
0.3
0.4
-2
10
0.5
0.6
0.7
time
The recovered OFDM signal
0.8
0.9
1
-6
x 10
1000
500
15
20
25
SNR (dB)
30
35
40
Figure 7: SER performance of the original, clipped, and recovered
OFDM signal using proposed method of OFDM -256QAM
Crosscorrelation function was measured between the
transmitted and received signals. Maximum peak of this
function showed the time delay between the lead and lag
signals. Figure 8 shows the maximum peak of the
crosscorrelation function equal to 63. There is a delay
produced in this simulation system was generated from
the reconstruction filtering process, the reconstruction
filter produced the delay that was enough to impede the
reception and caused the slight difference between the
transmitted signal and the received signal. For this system,
the delay produced by the reconstruction and
demodulation filters is about:
63
Td =
= 7.0314×10-9 sec
SP
where SP is the simulation period = 4× fc
-500
-1000
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
time
c o rre la t io n w it h o u t n o rm a liz a t io n
10
0
-6
x 10
9
20
x 10
15
10
5
0
-5
0
100
200
300
400
500
600
700
800
lag
Figure 8: Crosscorrelation of the transmitted and recovered signals
With the proposed method of recovering the clipped
part of the original signal, it is possible to use low CR to
achieve a good PAPR reduction, but the value of CR
depends on the order of the modulation scheme. Figures
9, 10, and 11 show the CCDF of the normal and the
recovered OFDM signals at different CR with different
modulation schemes. The improvement in PAPR at the
probability of 10-3 is listed in table 3 at different CR
values.
0
10
-1
CCDF(Pr(PAPR>PAPR0))
5
a m p lit u d e
Original OFDM signal
Clipped signal (CR=1.3)
Recovered signal (CR=1.3)
Clipped signal (CR=1.3)
Recovered signal (CR=2.4)
-3
10
10
-2
10
-3
Original OFDM signal
Clipped signal (CR=1)
Clipped signal (CR=2.5)
10
2
4
6
8
10
PAPR0(dB)
12
14
16
Figure 9: CCDF of PAPR for normal and clipped OFDM signal at
different CR with 16-QAM
IJCSNS International Journal of Computer Science and Network Security, VOL.9 No.7, July 2009
43
value of EVM at low SNR values better than the normal
OFDM system in figure 12.
0
10
20
CCDF(Pr(PAPR>PAPR0))
16-QAM
64-QAM
256-QAM
18
-1
10
16
14
12
-2
EVM (%)
10
10
8
-3
Original OFDM signal
clipped signal (CR=1.1)
clipped signal (CR=3.5)
10
4
6
8
10
PAPR0(dB)
6
4
12
14
16
2
Figure 10: CCDF of PAPR for normal and clipped OFDM signal at
different CR with 64-QAM
0
5
10
15
20
25
SNR (dB)
30
35
40
Figure 12: EVM-SNR of different types of normal (unclipped) OFDM
signal
0
10
28
16-QAM
64-QAM
256-QAM
26
24
22
EVM (%)
CCDF(Pr(PAPR>PAPR0))
-1
10
-2
10
20
18
16
-3
Original OFDM signal
Clipped signal (CR=1.2)
Clipped signal (CR=3.4)
10
4
6
8
10
PAPR0(dB)
14
12
12
14
16
10
Figure 11: CCDF of PAPR for normal and clipped OFDM signal at
different CR with 256-QAM
CR=2.5
CR=1.1
CR=3.5
CR=1.2
CR=2.5
7.24
11.86
4.22
11.31
4.47
10.66
The measurement is carried in a channel with different
distortion which has different SNR. Error vector
magnitude (EVM) is far greater than SER. In the case of
high SNR, SER is nearly equal to zero which could not
fully characterize signal distortion of system. Obviously,
it is incapable to pursuit perfect system, while EVM still
has high enough value which contains more information
and could characterize the imperfection of system. The
proposed recovering solution in figure 13 shows small
15
SNR (dB)
20
25
16
16-QAM
64-QAM
256-QAM
14
12
10
EVM (%)
CR=1
10
Figure 13: EVM-SNR of different types of conventional clipped signal
with CR=1.1
TABLE 3: PERCENTAGE OF THE CLIPPED OFDM SAMPLES AT
DIFFERENT CLIPPING RATIO VALUES
Reduction in the PAPR at the probability of 10-3 compared to the
normal OFDM with:
16-QAM (dB)
64-QAM (dB)
256-QAM (dB)
5
8
6
4
2
0
5
10
15
SNR (dB)
20
25
30
Figure 14: EVM-SNR of different types of recovered signal with
CR=1.1
IJCSNS International Journal of Computer Science and Network Security, VOL.9 No.7, July 2009
44
4. Conclusion
The proposed method to recover the original signal by
copying the clipped part of the original signal at the
transmitter side and then provide this copied signal to the
receiver as information data. The numerical results show
the ability of this method to eliminate the clipping noise
and improve the SER performance compared to the
conventional clipped signal and even better than the SER
performance of unclipped OFDM system. It is possible to
use low CR with this proposed method to get efficient
PAPR reduction. But it is important to make appropriate
selecting of the CR to minimize the amount of the
transmitted copies of the clipped parts of the original
OFDM signal to avoid wasting the valuable bandwidth.
[10]
[11]
[12]
[13]
Acknowledgment
This research work was partially supported by
PKT4/2008 research grant. The authors would like to
thank the project leader and appreciate his kindness,
valuable assistance, and financial support.
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Ibrahim Ismail Al-kebsi received the
B.Sc.
degree
in
electronic
and
communication engineering from University
of Technology, Baghdad, IRAQ, in 2000.
He received the M.Sc. degree in computer
and communication engineering from
University Kebangsaan Malaysia, Bangi,
Malaysia, in 2005. He is currently a PhD
student at university Kebangsaan Malaysia
(UKM). His research interests are signal
processing in communications especially in multicarrier systems
(OFDM), wireless communication systems.
IJCSNS International Journal of Computer Science and Network Security, VOL.9 No.7, July 2009
Mahamod Ismail received the B.Sc.
degree in Electrical and Electronics from
University of Strathclyde, U.K. in 1985,
the M.Sc. degree in Communication
Engineering and Digital Electronics from
UMIST, Manchester U.K. in 1987, and the
Ph.D. from University of Bradford, U.K.
He is currently a Professor with the
Department of Electrical, Electronics and
System Engineering. His research interests include mobile
communication and wireless networking. He is also actively
involved in conference and became the Technical Program
Chairman, technical committee and paper reviewer.
Kasmiran Jumari received the B.Sc.
degree from Universiti Kebangsaan
Malaysia in 1976. He received the M.Sc.
degree from University of Aberdeen in
1977. He received the PhD degree from
University of Kent, UK, in 1985. He is now
a professor at the Department of Electrical,
Electronic and System Engineering,
Universiti Kebangsaan Malaysia, Bangi,
Malaysia. . His main research interests include network security,
and image processing.
Tharek Abd. Rahman received the B.Sc.
degree from University of Strathclyde,
UK, in 1979. He received the M.Sc.
degree from UMIST, Manchester, UK, in
1982. He received the PhD degree from
University of Bristol, UK (1988), in
1985. He is now a professor at the
Department of Radio Communication
Engineering, Faculty of Electrical
Engineering, Universiti Teknologi Malaysia. His research
interests include mobile communication and wireless networking.
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